1. Field of the Invention
The invention relates to toughened styrene/acrylonitrile polymer compositions containing a halogenated monoolefin/alkylstyrene copolymer.
2. Description of Related Art
Styrene/acrylonitrile (SAN) copolymers are well known resins having extremely good weatherability (resistance to UV attack) which makes them extremely useful in the production of molded articles for applications such as automotive or marine body parts, packaging and building panels. However, these resins possess relatively poor room temperature impact properties, thereby limiting their use in many such applications requiring good impact strength.
The impact properties of SAN copolymers have been improved by incorporating up to about 20 wt % polymerized butadiene by free radical copolymerization of styrene and acrylonitrile in the presence of dispersed or dissolved polybutadiene to form ABS graft copolymer compositions. The ABS resins exhibit a marked increased in impact properties, but at the cost of diminished weatherability because the residual unsaturation present in the polybutadiene molecular structure is susceptible to U.V. and ozone attack.
Yet another approach in modifying SAN impact properties is to form blends or graft blends of SAN with chlorinated polyethylene, as for example disclosed in U.S. Pat. Nos. 3,658,950, 4,341,884 and 4,794,143. However, these methods incorporate excessive amounts of halogen into the composition which is undesirable in many applications.
SAN properties have also been modified by polymerizing styrene and acrylonitrile in the presence of a C.sub.4 -C.sub.7 isomonoolefin copolymer containing an unsaturated conjugated diene (prepared by dehydrohalogenating halogenated butyl rubber), as for example disclosed in U.S. Pat. No. 4,143,098, or in the presence of a pre-crosslinked bromobutyl rubber, as disclosed in U.S. Pat. No. 4,026,968. However, these resulting compositions containing ethylenically unsaturated components may also be susceptible to U.V. or ozone attack.